The present invention relates to a semiconductor switching circuit and, more particularly, to a semiconductor switching circuit suited for, e.g., an SPnT (Single-Pole n-Throw) switching circuit.
For example, an SP3T switch is widely used as a switch for switching transmission and reception of radio-frequency signals by a single antenna in a cellphone.
This radio-frequency switch of 1 GHz or more is in many cases made of a compound semiconductor such as GaAs having high electron mobility and excellent characteristics in a radio-frequency region.
Unfortunately, a P-channel FET is difficult to realize by the compound semiconductor. Therefore, when logic circuits necessary to control switching are to be fabricated by using OR circuits, they are fabricated by using, e.g., N-channel FETs alone, N-channel FETs and resistors, or N-channel FETs and diodes. In any case, current consumption occurs in a standby state.
If it is necessary to reduce this current consumption in the standby state to zero, the logic circuits must be fabricated by using externally attached CMOS circuits. In this case, however, six control terminals are necessary.
This increases the number of pads and inevitably increases the chip size. The increase in chip size is a fatal problem in a switching IC which is severely required to reduce the fabrication cost.
Also, it is necessary to form many interconnections on a packaging substrate, and form an additional logic IC for control. This increases both the packaging area and cost.
The conventional SP3T switch, therefore, must incorporate OR circuits, and this increases the current consumption.
As described above, it is difficult for the conventional shunt type SP3T switch to decrease the number of control terminals to three or less and at the same time reduce the current consumption in the standby state.
A reference disclosing the conventional semiconductor switching circuit is as follows.
Japanese Patent Laid-Open No. 2000-68807